In recent years, a technology to synthesize substances without using substances having much effects on environment such as organic solvents is required. When a gas such as CO2 is maintained at a point higher than a critical point, it is converted into a supercritical state in which there is no boundary between gas and liquid. A substance in the supercritical state is a fluid which is neither liquid nor gas, and is referred to as a supercritical fluid.
Downsizing of integrated circuits is in steady progress. In the related art, a super-micro-fabrication process such as manufacture of the integrated circuits is generally performed with a dry process (vacuum process) in vacuo, a rarefied gas environment, or a plasma discharge environment.
The dry process has been developed as an extremely effective measure because independent atomic elements or molecules, or ions thereof can be used directly for processing. However, in the vacuum process, maintenance of vacuum and generation of plasma increase the cost. In a wet process in which a liquid is used for plating or cleaning, a large quantity of waste liquid is generated, which presents a serious environmental problem.
The supercritical fluid using CO2 as a medium has a property between liquid and gas, and has peculiar properties such that surface tension is zero and the capability to dissolve other substances (solvation capability) is high. In addition, it also has advantages such as chemical stability, inexpensiveness, harmless, and low cost. In addition, there are many characteristics such that recycling of CO2 in itself and substances dissolved in CO2 fluid by vaporization and reliquefaction.
In an integrated circuit manufacturing process, study and development of using the supercritical CO2 are in progress mainly in a wafer cleaning process. For example, in a cleaning process, a process aiming at the salvation energy, the safety and recycling capability of the supercritical CO2 has been developed. The study and development of a micro-fabrication process for forming a nano-level wiring are also in progress taking advantage of the fact that the surface tension is zero in the supercritical CO2.
For example, a main function in manufacture of semiconductor devices is the formation of a thin film, and Rapid Expansion of Supercritical Solution is known as a method of forming a thin film using a supercritical fluid. D. Matson et al disclose a technology of expanding a supercritical fluid containing a source material dissolved therein and forming a supersaturated raw material. A further developed technology is a method of obtaining a thin film of a metal oxide by dissolving an oxide complex in a supercritical fluid and blowing the same onto a heated substrate (see Patent Document 1: JP 2003-213425 A)
The inventors have uniquely developed a method of forming a thin film by dissolving a thin film forming raw material such as an organic metal in a supercritical CO2 and allowing it to undergo a film forming reaction in that state (E. Kondoh and H. Kato, Microelectron. Eng. Vol. 64 (2002), pp. 495), and applies the method to the manufacture of integrated circuit wirings such as filling Cu into via holes or trenches, and the formation of a Cu diffusion barrier layer (Japanese Patent Application No. 2003-17948, “Method of manufacturing semiconductor devices”, and Japanese Patent Application No. 2003-17949 “Method of manufacturing semiconductor devices”) The similar method is disclosed also in JP 2003-514115 T.
In the processing in a supercritical fluid, addition of a gas as a source material is frequently performed. For example, when decomposing a harmful organic substance such as dioxin using oxidative reaction in a supercritical water instead of burning, an oxidizing gas such as oxygen or air as an oxidizer is used in addition to the supercritical water. It is pointed out that addition of the gas to a supercritical CO2 is necessary when performing coating of fine particles efficiently by the Rapid Expansion of Supercritical Solution (see Patent Document 1: JP 11-197494 A).
When depositing a thin film using a reaction in a supercritical fluid, addition of a gas is further important. For example, the inventors have developed a technology of dissolving Cu (hfac)2, a metal complex, in a supercritical fluid, adding H2 thereto to produce a reduction reaction to obtain a Cu thin film, and proved that when H2 is not added, only the particles are produced, and a thin film is not formed (Report introduced above). In order to deposit a thin film, it is necessary that a heterogeneous reaction occurs continuously on the substrate surface and developing surfaces. In order to cause the reaction to occur on the substrate surface by priority, the substrate surface is required to act catalytically. In the case of precipitation of Cu, the substrate metal aids dissociation of H2.
The inventors developed a technology to obtain a ruthenium oxide (RuO2) thin film by dissolving bis(cyclopentadienyl)ruthenium (RuCp2) as a metal complex in a supercritical fluid and causing an oxidative reaction with ozone gas (O3) added simultaneously (Japanese Patent Application No. 2004-167782). Ozone, being unstable and dissociating on the substrate surface by priority to liberate oxygen atom, reacts easily with the metal precursor, so that the ruthenium oxide is deposited.    Patent Document 1: JP 2003-213425 A    Non-Patent Document 1: J. Mater. Sci. Soc. Vol. 22, No. 6, 1918 (1987)    Patent Document 2: JP 2003-514115 T    Patent Document 3: JP 11-197494 A